Optical system driving device

ABSTRACT

An optical system driving device, includes: a carriage on which an objective lens is mounted; a guide for slidably supporting the carriage to guide the carriage in a tracking direction; at least a pair of coils which are attached to both sides of the carriage and which are wound in a direction perpendicular to a plane including the tracking direction and an optical axis of the objective lens; and at least a pair of magnet sections which are opposed to the coils so as to sandwich the carriage, wherein each of the pair of magnet sections has a permanent magnet in which two magnetic poles are arranged in a direction perpendicular to the plane including the tracking direction and the optical axis of the objective lens, and the two magnetic poles of one permanent magnet are arranged in an opposite direction of the two poles of the other permanent magnet.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical system driving device. Inparticular, the present invention relates to an optical system drivingdevice mounted to a pickup apparatus for reading CD, DVD or the like.

2. Description of Related Art

An optical system driving device mounted to a pickup apparatus isarranged to move an objective lens in a tracking direction by usingelectromagnetic power (see for example Japanese Patent Laid-OpenPublication No. 8-87765). Specifically, as shown in FIG. 4, an opticalsystem driving device 100 includes an objective lens 101 and a carriage102 on which the objective lens 101 is mounted. The carriage 102 isslidably supported by a pair of guides 103. The guide 103 is providedalong the tracking direction. When the carriage 102 is slid along theguide 103, the objective lens 101 is moved along the tracking direction.

Coils 104 are fixed at both side faces of the carriage 102 so that thewinding direction of the coils are along the tracking direction. Aninner yoke 105 is inserted into the coil 104 in parallel with the guide103. At an exterior of the inner yoke 105, an outer yoke 106 is providedso that the outer yoke 106 and the inner yoke 105 form a frame. At aninterior of the outer yoke 106, a bar permanent magnet 107 is providedalong the inner yoke 105.

When current flows in the coil 104, electromagnetic power is generatedbetween the coil 104 and the permanent magnet 107. The electromagneticpower causes the carriage 102 to move along the guide 103, and theobjective lens 101 is moved in the tracking direction. When currentflowing in the coil is controlled, a position control of the objectivelens 101 is performed.

Due to the above structure, during the movement, the coil 104 itselfeasily resonates. When the resonant is caused, the position control ofthe objective lens becomes unstable.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above problem. Anobject of the present invention is to suppress the resonance of the coiland to improve the accuracy of the position control of the objectivelens.

According to one aspect of the present invention, an optical systemdriving device, comprises:

a carriage on which an objective lens is mounted;

a guide for slidably supporting the carriage to guide the carriage in atracking direction;

at least a pair of coils which are attached to both sides of thecarriage and which are wound in a direction perpendicular to a planeincluding the tracking direction and an optical axis of the objectivelens; and

at least a pair of magnet sections which are opposed to the coils so asto sandwich the carriage,

wherein each of the pair of magnet sections has a permanent magnet inwhich two magnetic poles are arranged in a direction perpendicular tothe plane including the tracking direction and the optical axis of theobjective lens, and

the two magnetic poles of one permanent magnet are arranged in anopposite direction of the two poles of the other permanent magnet.

Preferably, the optical system driving device further comprises:

a frame for retaining the permanent magnets and the guide;

a frame guide for slidably supporting the frame to guide the frame inthe tracking direction; and

a transfer mechanism engaged with the frame to transfer the frame in thetracking direction.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description and the accompanying drawings given hereinafter,which are for illustration purpose only, and thus are not intended tolimit of the scope of the present invention, and wherein:

FIG. 1 is a perspective view for schematically illustrating thestructure of an optical system driving device of this embodiment;

FIG. 2 is a perspective view for schematically illustrating thestructure of the first transfer mechanism provided in the optical systemdriving device of FIG. 1;

FIG. 3 illustrates a positional relation between a coil provided in thefirst transfer mechanism of FIG. 2 and a permanent magnet; and

FIG. 4 is a perspective view for schematically illustrating thestructure of a conventional optical system driving device.

PREFERRED EMBODIMENT OF THE INVENTION

Hereinafter, an optical system driving device in this embodiment will bedescribed with reference to the drawings. FIG. 1 is a perspective viewfor schematically illustrating the structure of an optical systemdriving device 1 of this embodiment. As shown in FIG. 1, the opticalsystem driving device 1 comprises: the first transfer mechanism 3 forfinely adjusting the position of an objective lens 2; the secondtransfer mechanism 4 for moving the objective lens 2 in the entiretravel range in the tracking direction A prior to the fine adjustment bythe first transfer mechanism 3; and a control section (not shown) forcontrolling the first transfer mechanism 3 and the second transfermechanism 4.

FIG. 2 is a perspective view for schematically illustrating thestructure of the first transfer mechanism 3. As shown in FIG. 2, thefirst transfer mechanism 3 comprises: a carriage 5 on which theobjective lens 2 is mounted; a pair of guides 6 that slidably supportthe carriage 5 to guide the carriage 5 in the tracking direction A; apair of coils 7 attached to both sides of the carriage 5; and a pair ofmagnet sections 8 that are opposed to the coils 7 so as to sandwich thecarriage 5.

In this embodiment, the coil 7 is previously wound to have apredetermined size and the wound coil 7 is fixed to the carriage 5. Whenthe carriage 5 has a boss and the coil 7 is attached to the boss, thecoil 7 can be accurately positioned.

On the contrary, when the coil 7 is wound around the boss of thecarriage 5, the carriage 5 and the coil 7 are used as a single member inwhich the carriage 5 is integrated with the coil 7, in the assemblysteps. Thus, the number of the assembly steps can be reduced.

FIG. 3 illustrates a positional relation between the coil 7 and themagnet section 8. As shown in FIG. 3, a pair of magnet sections 8comprises at least a pair of permanent magnets 81 in which two magneticpoles are arranged in a direction B perpendicular to the trackingdirection A (the direction B is perpendicular to a plane including thetracking direction A and an optical axis of the objective lens 2.). Thepair of permanent magnets 81 are placed so that two poles of onepermanent magnet are arranged in an opposite direction of two poles ofthe other permanent magnet. The coil 7 is also wound along the directionB perpendicular to the tracking direction A. By winding the coil 7 inthe manner as described above, a wire S which is wound so as to form aplurality of layers at the base of the coil 7 is fixed to the carriage5.

When current flows in the coil 7, electromagnetic power is generated inthe coil 7 to move the coil 7 in the tracking direction A. Specifically,when current flows in an upper part of the coil 7 in a direction fromthe front side to the rear side (direction J1) and current flows in alower part of the coil 7 in a direction from the rear side to the frontside (direction J2), the coil 7 is moved in the tracking direction A1.When current flows in the upper part of the coil 7 in a direction fromthe rear side to the front side (direction K1) and current flows in thelower part of the coil 7 in a direction from the front side to the rearside (direction K2), the coil 7 is moved in the tracking direction A2.By the movement, the carriage 5 is moved along the guide 6. Therefore,it is possible to carry out the position control of the objective lens2.

As shown in FIG. 1, the second transfer mechanism 4 comprises a frame 9for retaining a magnet section 8 and a guide 6 of the first transfermechanism 3; a frame guide 10 for slidably supporting the frame 9 toguide the frame 9 in the tracking direction A; and a sending mechanism11 that is engaged with the frame 9 to move the frame 9 in the trackingdirection A.

In the sending mechanism 11, a link section 12 in which a plurality ofteeth (not shown) are formed along the tracking direction A, is providedso as to be fixed to one side of the frame 9. The sending mechanism 11comprises a lead screw 13 that is provided in the tracking direction Aand that is engaged with the teeth of the link section 12; and a motor14 for rotating the lead screw 13. When the motor 14 rotates the leadscrew 13, the frame 9 is moved via the link section 12 in the trackingdirection A. The lead screw 13 has a length that is at least equal to orlonger than the travel range of the objective lens 2. Therefore, theframe 9 can move within the travel range of the objective lens 2 in thetracking direction A along the frame guide 10. It is possible to carryout the position control of the objective lens 2.

Electromagnetic power is generated only in a range of the size of thecoil 7. Thus, in order to supply electromagnetic power to the entiretravel range, the coil 7 must be sized to cover the travel range. Such alarge-sized coil 7 is not desirable because much material of the coil isrequired and an increased weight of a movable portion, an increasedresistance value, and a deteriorated strength for example, are caused.In the structure of the optical device, the entire travel range ismanaged by another sending mechanism and the section in which the highaccuracy and high responsiveness are required at the final stage ismanaged by electromagnetic power.

Although the sending mechanism 11 is described as a mechanism using alead screw, a mechanism in which the objective lens can be moved at ahigh speed, may be applied to the sending mechanism. For example, atransfer mechanism other than a stepping motor, e.g., the so-calledSIDM® using a piezoelectric element, an ultrasonic motor, or shapememory alloy or the like can be applied. By the sending mechanism, theobjective lens is roughly moved, and the high accurate movement controlis not required. Thus, the mechanism having a simple movement controlfunction can be applied to the sending mechanism.

Next, an operation of this embodiment will be described.

During the position control of the objective lens 2, the control sectionfirstly controls the second transfer mechanism 4 to move the objectivelens 2. At the same time, the control section controls the motor 14 torotate the lead screw 13 and to move the frame 9 in the trackingdirection A. Thereafter, the control section stops the motor 14 so thatthe frame 9 stops in the vicinity of a predetermined tracking position.The movement of the objective lens 2 by the second transfer mechanism 4is finished.

Thereafter, the control section controls the first transfer mechanism 3to move the objective lens 2. At the same time, the predeterminedcurrent flows in the coil 7. As a result, electromagnetic power isapplied between the coil 7 and the magnet section 8. By theelectromagnetic power, the carriage 5 is moved along the guide 6 in thetracking direction A. Thereafter, by the control section, the currentflows in the coil 7 so that the objective lens 2 tracks a predeterminedposition on a disk to perform the movement of the objective lens 2 bythe first transfer mechanism 3.

As described above, according to this embodiment, the coils 7 wound inthe direction B perpendicular to the tracking direction A are attachedto both sides of the carriage 5. Thus, the direction along which thecoil 7 is wound is perpendicular to the tracking direction A. Byattaching the coil 7 to the carriage 5 in this manner, the wire S whichis wound so as to form a plurality of layers at the base of the coil 7is fixed to the carriage 5. Thus, it is difficult to deflect the coil 7and the strength of the coil 7 is increased. Because the ratio of thefixing area for the coil 7 to the entire coil 7 is increased and thestrength thereof is increased as described above, the resonance of thecoil 7 can be suppressed. Therefore, the stability of the coil 7 iseasily maintained. Further, the position control of the objective lens 2can be performed with a higher accuracy.

Furthermore, because the frame 9 is moved in the tracking direction A bythe sending mechanism 11 of the second transfer mechanism 4, thetracking position of the objective lens 2 is roughly adjusted. Afterthis position adjustment of the second transfer mechanism 4, thecarriage 5 is moved in the tracking direction the electromagnetic powerbetween the coil 7 of the first transfer mechanism 3 and the magnetsection 8. Therefore, the tracking position of the objective lens isfinely adjusted.

As described above, an embodiment of the present invention has beendescribed. However, the present invention should not be construed so asto limit the present invention to the above embodiment and also may beappropriately changed or modified. For example, the above-describedembodiment also may be arbitrarily combined with a modified example.

The entire disclosure of a Japanese Patent Application No. 2006-110829filed on Apr. 13, 2006, including specification, claims, drawings andsummary are incorporated herein by reference in their entirety.

1. An optical system driving device, comprising: a carriage on which anobjective lens is mounted; a guide for slidably supporting the carriageto guide the carriage in a tracking direction; at least a pair of coilswhich are attached to both sides of the carriage and which are wound ina direction perpendicular to a plane including the tracking directionand an optical axis of the objective lens; and at least a pair of magnetsections which are opposed to the coils so as to sandwich the carriage,wherein each of the pair of magnet sections has a permanent magnet inwhich two magnetic poles are arranged in a direction perpendicular tothe plane including the tracking direction and the optical axis of theobjective lens, and the two magnetic poles of one permanent magnet arearranged in an opposite direction of the two poles of the otherpermanent magnet.
 2. The optical system driving device of claim 1,further comprising: a frame for retaining the permanent magnets and theguide; a frame guide for slidably supporting the frame to guide theframe in the tracking direction; and a transfer mechanism engaged withthe frame to transfer the frame in the tracking direction.